Characterization and modeling of microwave plasmas used for materials processing

Detailed models of the behavior of both charged and neutral species in nitrogen afterglows and hydrogen/argon discharges were developed in this study. Mass continuity equations were solved to investigate the dominant transport and rate processes in a low-pressure, non-isothermal nitrogen afterglow. Electron density and N-atom flux were measured as a function of position in the afterglow and compared with model results. It was found that the model, with no adjustable parameters, yielded very good agreement with experimental measurements. The radial gradient of N-atom concentration was shown to be insignificant, which reduced the model to a one-dimensional mass continuity equation. However, the model of charged species behavior must be carried out in two dimensions. Wall recombination play a very important role for both neutral and charges species while the homogeneous recombination can be ignored.; A volume-averaged model coupling species and power balance equations was developed to predict the electron temperature and species concentration as a function of operating parameters in a pure hydrogen discharge. It was found that the pressure, power, flow rate, reactor radius, and gas temperature all affect the generation of H-atoms. Electron temperature is mainly determined by the gas pressure.; Finally, the effect of argon addition on a hydrogen discharge was studied. The model results showed that the argon addition increases the electron density through direct ionization of ground state Ar, which in turn, enhances the degree of hydrogen dissociation. It was also found that the plasma retains the basic properties of a hydrogen plasma even for mixtures containing 90% Ar. Electron temperature and H-atom concentration are only slightly changed with argon addition, and the dominant ionic species is still H{dollar}sb3sp+.{dollar}...